Actuators the stability or stabilities of which are provided by one or more magnets are known in the prior patent art. For example, U.S. Pat. No. 4,779,582 proposes topologies of actuators for moving automobile valves and which in particular use magnets at the fixed (stator) part that actively participate in the maintenance of the two extreme positions of the actuator. These magnets are positioned between two separate electrical coils in order to allow looping of the magnetic flux around the first or second coil. The same type of actuator topology can be found in the document EP 0157632 or more recently in the document WO 2014/023326.
The object of these devices is to solve the general problem of providing mono- or bi-stability without any mechanical aid, such as springs, and this without the consumption of electrical energy by virtue of the use of permanent magnets. However, these devices do not make it possible to provide an easy leaving of the stable positions. This is because springs are used to allow easier leaving, or stripping, of the stable positions. An electric current in the coil, in a privileged air circulation direction, makes it possible to assist stripping but does not completely cancel out the holding force generated by the magnets or does not allow sufficient stripping force to overcome any friction or a load applied to the movable part. In addition, using two separate coils on either side of these magnets in the central position makes the actuator ineffective, half of the total winding not being magnetically active when the movable part is at one end or other of the travel of the actuator.
Another type of mono- or multi-stable actuator making it possible to keep these stability positions by means of the action of a magnet carried by the movable part of the actuator is also known in the document WO 2004/066476. This actuator partly improves the previously mentioned actuators in that the whole of the electrical coil participates in generating a force, whatever the position of the movable part over the travel. In addition, the topology developed makes it possible to generate a stripping force that may be maximised by acting on the embedding of the magnets on the movable part, guided by the mathematical equations disclosed in the document.
On the other hand, this actuator has an original topology that requires an axial space requirement (in the direction of the movement) that may be great, all the more so when the travel required is great. This is because the axial space requirement of the actuator will at a minimum be equal to twice the travel plus what is necessary for installing the electrical coil and the ferromagnetic poles on the stator, as can be appreciated in FIG. 6 of this document. In addition, moving magnets that will undergo high accelerations due to impacts during the arrival of the movable part in the extreme positions, which may in the long term be detrimental to the service life of the system, may possibly be criticised.
Finally, an actuator topology is also known that may have a bistable character where the magnets are fixed in the magnetic structure, requiring only one electrical coil for the functioning in both actuation directions, and where the movable part consists only of a ferromagnetic piece, as described in the applications WO 9427303 or WO 2015/114261. Since these topologies, through their nature, do not benefit from a very high stripping force, summary indications are given to allow an increase in this force by virtue of the use of pole pieces.
Though this type of structure makes it possible to partly settle the aforementioned problems (through the use of a fixed magnet and the use of pole pieces), no precise teaching is given as to the use of the pole pieces. In addition, the dimensional rules given in these documents and particularly the document EP 0713604 make this actuator, as indicated in its preamble, intended for travels of small amplitude, around +/−1 millimetre. There therefore exists a need, not solved by the prior art, relating to the production of an actuator having a travel of several millimetres and being able to range up to typically 15 to 20 millimetres, minimising the magnet mass, favouring a purely magnetic stripping force sufficient to overcome the stable holding force, the friction and any external loads applied to the moving part of the actuator, and favouring a significant actuation force over the travel of the actuator.